I insisted on doing it with Sturgian axemen. I formed a line at the beginning and let them throw, killing the first group quite easily. Then I advanced in a shield wall and held the one side of the bridge- I used my drilled axe to kill most of them while they smacked my men's shields. Then I advanced to the gate house and did the same thing. I kept my shield wall tight to one side so they wouldn't get flanked.
After that I brought my men up the walls to a defendable spot where the range couldn't hit us and used a bow to get the groups to attack us one at a time. Having no bow skill, this took awhile.
But I did have to kill most of the men myself, and when I finally did it it was very close- I think I had one man left. It also took me about 6 tries, tho two of them were in the morning before the coffee kicked in and I couldn't block at all and kept missing lol.